1. Field of the Invention
The present invention relates to the field of rotary winged aircraft and in particular to main rotor systems in a helicopter with a tiltable rotor.
2. Description of the Prior Art
Helicopters with pitch cone rotors have long been the subject of intensive development and have exhibited many desirable flight characteristics. For example, helicopters with pitch cone coupling have been found to respond smoothly to the application of collective control thereby giving a cushioned response as opposed to an abrupt vertical movement to the aircraft which is typical of collective pitch controls in other types of rotor systems. Positive lateral and longitudinal stability with pitch cone coupled rotors are also outstanding when compared with current operational helicopters. The ability to turn up and shut down in high winds and the absence of ground resonance tendencies are further among the advantages of a pitch cone rotor. Hover stability and dynamic longitudinal stability are outstanding as well. However, the design of direct shaft-driven pitch cone rotor systems has not been successful. Most pitch cone rotor systems under active development have used tip jet powered rotors because of an unacceptible two per revolution torque oscillation which is characteristic when a shaft-driven rotor hub is tilted. Examples of development of such prior art pitch cone rotor systems are described in detail in the Navy Evaluation of the model 120 helicopter, Project TED No. PTRAC/42101.1, Naval Air Test Center, Patuxent River, Md., and in the Phase Two Flight Evaluation, Air Force Flight Test Center, TR-56-35, Edwards Air Force Base, Calif.
Therefore, what is needed is some means by which a rotor hub can be directly shaft-driven in a pitch cone rotor design.